HS2 launches final viaduct on the approach to Curzon Street Station

Engineers on High Speed 2 (HS2), Britain's new high-speed railway, have launched the first 170 m of the Duddeston Junction Viaduct over the Birmingham to Derby railway lines. HS2 says the operation is the opening phase of a crossing of six tracks — three freight and three passenger — on the final approach to Birmingham Curzon Street Station, and is expected to conclude next summer.

The structure is one of five interconnecting viaducts known as the Curzon Approaches, which weave through Birmingham's industrial corridor into the city centre. HS2 describes Duddeston Junction as the first and longest in that series, while Tony Zakaria, HS2's senior project manager for the Curzon Approaches, describes the launch as that of the fifth and final viaduct on the Curzon Approaches. The two are reconcilable: it is the last of the five to be launched across the existing railway, and the first that trains will cross travelling towards Curzon Street.

Duddeston Junction Viaduct is approximately 700 m long, making it the longest structure on the Curzon Approaches by more than 400 m — Curzon 1, the next longest, measures around 300 m. HS2 gives the length as 700 m and BBV's section manager as 705 m. It is formed from weathering steel and, on HS2's figures, comprises 14 spans of around 55 m with a cumulative weight of up to 6,835 tonnes.

HS2 singles the structure out for its geometry rather than its appearance: where the neighbouring Curzon 2 Viaduct is the visually striking one, Duddeston Junction is the technically demanding one. It follows a continuously varying horizontal curve and climbs on a 3% gradient, lifting the alignment from ground level to around 12 m above the existing tracks. HS2 says this makes construction, logistics and alignment control significantly harder.

The site is among the most constrained on the project. Up to 90 operatives and engineers are working in a narrow corridor between six live railway lines and a busy industrial estate. John Emery, senior sponsor at Network Rail, says the six lines carry a mixture of more than 200 passenger and freight services a day, and describes the corridor as one of the busiest in the region.

HS2's construction partner, Balfour Beatty VINCI (BBV), began enabling works in 2023, moving major utilities and tackling heavy ground contamination before diverting two of the three freight lines onto a new bridge and embankment to create a safe working space for the viaduct and its substructure. To move the freight lines, BBV built the Duddeston Mill Road Underbridge; working with Network Rail, the two lines were then realigned to establish a 20 m wide corridor between the existing tracks, with the realigned tracks crossing the new bridge to give the clearance HS2's construction needs.

The structure is being installed by incremental launching, which HS2 refers to as a slide technique. Each completed span is added to the rear of the assembly, which is then pulled forward over the railway corridor. Seven spans will be launched across the live tracks in this way; once the structure has cleared the railway, the seven remaining spans will be lifted and lowered into place by crane on the far side.

The viaduct is supported by one abutment, two steel piers, four portals — frames straddling the tracks below — and eight concrete piers. HS2, BBV and Network Rail are now planning the next major phase, crossing the three passenger lines, which is scheduled to begin in December.

Zakaria said the launch is a clear sign of progress in bringing high-speed rail to Birmingham, and that the "final mile stretch of the HS2 route into the city centre" is extremely challenging, planned in conjunction with Network Rail to minimise disruption to passenger and freight services. Ross Rendell, section manager at BBV, said the viaduct is being built inside a narrow space beside a live railway, curving above the industrial area on an incline, and that crossing six lines adds further difficulty.

Once the route is complete, trains will emerge from Bromford Tunnel and run in a cutting through Washwood Heath, then begin their ascent through Saltley on a retaining wall that connects to Duddeston Junction Viaduct. At that point the railway sits approximately 12 m above ground, giving clearance over the six lines below, before continuing towards Curzon Street Station.

The following is general engineering context rather than reported detail of this scheme. Weathering steel is specified on structures of this kind partly because the alloy develops a stable, adherent oxide layer that removes the need for a paint system, and therefore removes the need for repeated future access to maintain coatings above operational tracks. Incremental launching is chosen where possession of the ground beneath is impractical, since the deck is assembled at one abutment and pushed out over the obstruction. Combining a varying horizontal curve with a sustained gradient makes that considerably more demanding: the launch has to be guided around the curve while the self-weight component along a falling grade must be restrained, so temporary works, bearing and jacking arrangements and launch sequencing all carry more design effort than on a straight, level structure.